1. Field of the Invention
The present invention relates to a cyclic olefin addition copolymer which has a reactive silyl group having a specific structure, excels in optical transparency, heat resistance, and adhesion, and is capable of producing a crosslinked product having improved dimensional stability, solvent resistance, and chemical resistance. The present invention also relates to a process for producing the cyclic olefin addition copolymer, a crosslinking composition, and a crosslinked product and a process for producing the same.
The present invention further relates to an optically transparent material including the cyclic olefin addition copolymer. The present invention still further relates to applications of the optically transparent material such as a substrate film, a polarizing film, a surface protective film, a retardation film, a transparent conductive film, and a light diffusion film for a liquid crystal display device and an EL display device using the optically transparent material.
2. Description of Background Art
In recent years, use of optically transparent resins in the field of optical parts such as lenses or liquid crystal display parts such as backlights, light guiding plates, and substrates, for which inorganic glass has been used, has progressed accompanied by a demand for a decrease in weight and size and an increase in density.
However, further improvement of birefringence, heat resistance, hygroscopic resistance, solvent resistance, chemical resistance, dimensional stability, adhesion, mechanical strength, and the like has been demanded for the resin materials in addition to optical transparency.
As a material excelling in optical transparency. hydrogenated compounds of a ring opening polymer of cyclic olefin compounds or addition polymers of cyclic olefin compounds given below have been proposed.
(1) Hydrogenated Compound of Ring Opening Polymer of Tetracyclododecene or Norbornene Compound
Japanese Patent Application Laid-open No. 60-26024, Japanese Patent No. 3050196, Japanese Patent Application Laid-open No. 1-132625, Japanese Patent Application Laid-open No. 1-132626, Japanese Patent Application Laid-open No. 5-214079, etc.
(2) Addition Copolymer of Ethylene and Norbornene Compound or Tetracyclododecene Compound
Japanese Patent Application Laid-open No. 61-292601 and Makromol. Chem. Macromol. Symp. Vol. 47, 83 (1991)
(3) Addition Polymer of Norbornene Compound
Japanese Patent Application Laid-open No. 4-63807, Japanese Patent Application Laid-open No. 8-198919, published Japanese translation of PCT International Patent Application No. 9-508649, and published Japanese translation of PCT International Patent Application No. 11-505880
(4) Addition (Co)Polymer of Norbornene Compound Containing Alkoxysilyl Group
A. D. Hennis et al., Am. Chem. Soc. Polymer Preprint 40(2) 782 (1999), WO98/20394, and WO97/20871
Most of the polymers disclosed in (1) and (2) have insufficient heat resistance due to a low glass transition temperature of less than 200° C. Moreover, since these polymers are not crosslinked, these polymers have insufficient solvent resistance, chemical resistance, and dimensional stability.
Japanese Patent Application Laid-open No. 5-214079 describes a reactive silyl group-containing norbornene polymer obtained by hydrosilylation and hydrogenation of a polymer of norbornene monomers having an unsaturated bond in the side chain. However, this application neither describes nor suggests crosslinking of the polymer by utilizing a reactive silyl group. Specifically, solvent resistance, chemical resistance, and dimensional stability of this polymer are insufficient due to the absence of a crosslinked structure.
Moreover, since it is difficult to complete the hydrogenation, this polymer may be colored or deteriorate if oxygen is present at a high temperature.
The polymer disclosed in (3) has heat resistance. However, it is difficult to crosslink the polymer due to the absence of an alkoxysilyl group. This results in insufficient solvent resistance, chemical resistance, and dimensional stability.
The addition polymer disclosed in (4) has transparency and heat resistance and exhibits adhesion due to the presence of an alkoxysilyl group. However, Japanese Patent Application Laid-open No. 7-196736 neither describes nor suggests crosslinking of the polymer by utilizing a alkoxysilyl group. Specifically, since the polymer is not crosslinked, problems relating to solvent resistance, chemical resistance, and dimensional stability may occur.
A cyclic olefin addition copolymer containing a reactive sylil group and a crosslinked product of the copolymer obtained by using a photoacid generator are described in WO97/20871 and WO98/20394. However, in the case of a sheet or a film having a large thickness, it is difficult to obtain a uniform crosslinked structure by using a method of crosslinking the copolymer by irradiation using a photoacid generator, since the crosslinking reaction mainly proceeds only on the surface. In addition, since the crosslinking reaction proceeds by light if the photoacid generator is used, the copolymer must be shaded during storage or processing. This results in inferior handling capability.
The present inventors have conducted extensive studies to solve the above problems. As a result, the present inventors have found that a crosslinked product excelling in optical transparency, heat resistance, and adhesion, exhibiting improved dimensional stability, solvent resistance, and chemical resistance, and capable of improving fragility and preventing occurrence of cracks in the film can be obtained by using a composition comprising a cyclic olefin addition copolymer which has a reactive silyl group having a specific structure and a specific compound. This finding has led to the completion of the present invention.
The present inventors have prepared an optically transparent material capable of solving the above problems by using a film or a sheet including the composition.
A liquid crystal display device and an EL display device are formed by using various parts and materials. In the liquid crystal display device, a liquid crystal, a liquid crystal alignment film, a liquid crystal substrate, a transparent electrode, a color filter, a polarizing film, a light guiding plate, a transparent conductive film, a retardation film, a surface protective film, a light diffusion film, a prism sheet, a spacer, a sealant, and the like are used. A liquid crystal display device is completed by assembling these parts and attaching module parts such as a driver IC, a printed board, and a backlight. In the EL display device, electroluminescence (EL), a polarizing film, a retardation film, a transparent electrode, and the like are used. An EL display device is completed by assembling these parts.
A polarizing film divides incident light into two polarized components which intersect each other. The polarizing film allows one of the two polarized components to pass therethrough, and absorbes or disperses the other polarized component. As the polarizing film, a film obtained by causing molecules of a polyvinyl alcohol film or the like to be oriented in a specific direction and a dichromatic substance such as polyiodine or a pigment to be absorbed on the film is used. However, such a polarizing film has insufficient mechanical strength in the direction of the transmission axis and shrinks due to heat or moisture. Therefore, a surface protective film is generally provided on each side of the polarizing film as a protective layer.
The surface protective film must have low birefringence, heat resistance, low moisture absorption, mechanical strength, surface smoothness, high resolution, adhesion to a tackiness agent, and the like. Conventionally, a triacetyl cellulose (TAC) film which is manufactured by using a casting method and has low birefringence and excellent surface smoothness has been used as the surface protective film. However, the TAC film has insufficient durability, heat resistance, mechanical resistance, birefringence, and adhesion to a tackiness agent under high temperature and high humidity conditions. Therefore, a material exhibiting higher heat resistance has been demanded.
A retardation film is used in an STN liquid crystal display device in order to compensate for coloring caused by wavelength dependency of the refractive index due to twisting of a liquid crystal molecule. The retardation film must have uniform birefringence over the entire surface and show no change in optical characteristics even under severe high temperature and high humidity conditions in order to obtain a vivid color and a precise image. In the liquid crystal display device, the polarizing film is layered on the retardation film through an adhesive layer. As the retardation film, a stretched and oriented polycarbonate (PC) film is generally used. However, since the PC film has a photoelastic coefficient as large as 9×10−12 cm2/dyn, the birefringence of the PC film is excessively increased, becomes nonuniform, or is changed due to only a small amount of stress occurring during assembling or due to environmental changes. Moreover, since the PC film has low surface hardness, problems may occur when forming the film or assembling the device. Therefore, a novel material capable of replacing the PC film has been demanded.
A transparent conductive film has a structure in which a transparent conductive film is layered on a transparent film substrate. Excellent heat resistance, surface smoothness, optical characteristics, and moisture resistance are necessary for the transparent film substrate. Conventionally, polyethersulfone (PES) and polyarylate (PAR) have been used as the transparent film substrate. However, the PES film has inferior transparency and the PAR film tends to cause optical distortion to occur. Therefore, a complicated technique is necessary for obtaining a transparent optically uniform film.
A light diffusion film is layered on the backlight of the liquid crystal display device in order to diffuse light or improve brightness. The light diffusion film is generally formed by forming a fine pattern on the surface of a transparent sheet or film by embossing or applying a photocurable resin. As a substrate for the light diffusion film, PC or polyethyleneterephthalate (PET) has been used. However, the PC film may be easily damaged due to low surface hardness. This may cause transparency to be impaired when forming a fine pattern or assembling the display device due to damage to the film. Since the PET film has insufficient transparency, a liquid crystal display device using the PET film lacks luminance, whereby the image quality may be impaired. Moreover, since the PET film has insufficient heat resistance, it is difficult to form a uniform fine pattern due to occurrence of warping of the film when forming a fine pattern.
A prism sheet collects diffused light passing through the light diffusion film at an angle of view of the liquid crystal display device and improves brightness of the liquid crystal display device. The prism sheet is used for a large-screen color STN display and a color TFT display. The prism sheet is formed by providing the PC film with a prism angle. At present, further improvement of brightness of the liquid crystal display device by improving optical nonuniformity and light transmissivity has been demanded.
Various types of films with a thickness of about 10–500 μm used for the liquid crystal display device and the EL display device are formed of a transparent resin which satisfies characteristics necessary for each film. As the transparent resin, an acrylic resin such as polymethylmethacrylate, a polycarbonate (PC) resin, a polyethyleneterephthalate (PET) resin, a polyethersulfone (PES) resin, and a polyarylate (PAR) resin are used. However, the PC resin and the polyester resin have large birefringence. The acrylic resin exhibits insufficient heat resistance and moisture resistance. The heat resistance of the PES resin is limited to 160–170° C. or less.
As a substrate film for an antireflection film, a film formed of a transparent resin such as PET, PC, and polymethylmethacrylate (PMMA) is widely used. The antireflection film formed on such a film may be a single-layer film or a multi-layer film consisting of two or more layers. Reflection of light over a broader wavelength range can be prevented as the number of layers is increased. However, since transparency is decreased as the number of layers is increased, transparency of the substrate is particularly demanded. The antireflection film is mainly used for displays. If the antireflection film has high birefringence, it is difficult to obtain a fine image due to distortion of the image. Therefore, a uniform antireflection film having low birefringence over the entire film has been demanded.
An increase in the size of the screen, a decrease in weight, an increase in brightness of the screen, durability under severe conditions, and the like have been demanded for the liquid crystal display device and the EL display device. Therefore, films for liquid crystal display devices and EL display devices formed of a transparent resin having excellent characteristics in comparison with conventional transparent resins have been demanded.
A conventional resin film has problems relating to fragility, occurrence of cracks, and the like. In order to use a transparent resin film as the material for the liquid crystal display device and the EL display device, it is necessary to prevent occurrence of cracks when assembling the display device or using the resulting product to provide a material which can withstand physical impact.
The present inventors have found that a transparent resin obtained by the present invention can solve the above problems relating to conventional resins which have been utilized as the material for a film for display devices, such as cyclic olefin copolymer (ring-opening polymer) resin, polycarbonate (PC) resin, triacetylcellulose (TAC) resin, polyethersulfone (PES) resin, and terephthalate (PET) resin, and can be applied to an optically transparent material such as a substrate film, polarizing film, surface protective film, retardation film, transparent conductive film, and light diffusion film. This finding has led to the completion of the present invention.